This research project seeks to elucidate factors participating in retinal photoreceptor degeneration in goldfish (Carassius auratus) subjected to prolonged low temperature (cold-stress) and in recovery from this process. Retinal electrical function and structural integrity, at both light and electron microscopic levels, are dependent variables providing indices for evaluating degeneration and recover. These measures are used in experiments manipulating energy drain and hormonal balance in an effort to implicate or exclude reduction of metabolism and hormonal imbalance as vehicles by which cold-stress affects photoreceptor viability. Other experiments are designed to define degeneration decay functions against stressing temperature and to investigate the possibility that photoreceptor degeneration is secondary to dysfunction of the pigment epithelial cells of the retina and/or disruption of the interphotoreceptor matrix. In general, this project attempts to use the phenomenon under investigation, cold-stress induced photoreceptor degeneration, as a tool for elucidating factors limiting photoreceptor viability and function.